Communication systems employing optical fibers--particularly WDM systems--are among the most promising systems for achieving high data rate telecommunications. Basically, optical fibers are thin strands of glass capable of transmitting optical signals containing large amounts of information over long distances with very low loss. In essence, an optical fiber is a small diameter waveguide comprising a core having a first index of refraction surrounded by a cladding having a second (lower) index of refraction. Typical optical fibers are made of high purity silica with minor concentrations of dopants to control the index of refraction.
Connectors are important components in optical fiber communication systems. With the increasing use of optical fibers and associated optoelectronic devices such as lasers, light-emitting-diodes (LEDs), photodetectors, and planar waveguide devices, there is an increasing need for reliable optical connectors, optical switches, and aligners. The precision alignment of optical paths, either permanent or reconfigurable, between two mating devices is essential for maximum optical coupling efficiency. For example, in the interconnection of a single mode optical fiber, the alignment tolerance must be on the order of a few micrometers or less.
There is also a need for devices which can introduce precise, controllable misalignment of optical paths. Such devices can be used to attenuate lightwave signals. Variable optical attenuators are increasingly important in dense wavelength-division multiplexing (DWDM) optical fiber transmission systems. Variable attenuators are used to vary the amount of loss light experiences as it passes through the device, typical losses range from low loss (&lt;1 dB) to very high loss (&gt;30 dB). The loss mechanism for variable attenuators can be coupling loss between fibers, polarization loss, absorption loss, scattering loss, or any combination of these.
A variable attenuator based on coupling loss is typically composed of two fibers whose separation is mechanically controlled. As the separation between fibers increases, the amount of loss also increases (see for example, Benner et al, "Low-reflectivity in-line variable attenuator utilizing optical fiber tapers," J. Lightwave Technol., Vol 18, p 7, 1990). Variable attenuators based on polarization loss are composed of GRIN lenses to collimate light from the fiber, a plate or cell to rotate the polarization of the light, and a polarizer to introduce loss. See for example, U.S. Pat. No. 5,727,109 issued to Jing-Jong Pan et al. on Mar. 10, 1998. In-line variable optical attenuators using magnetically controlled displacement are disclosed in U.S. patent application Ser. No. 09/097,549 entitled "Magnetically Controlled Variable Optical Attenuation", filed by Espindola et al. on Jun. 15, 1998.
While it is possible to obtain the alignment of optical devices mechanically, e.g., by using a motor or gear device, the inherent slow operation and mechanical relaxation in such devices are significant drawbacks. It is desirable to have the alignment or optical switching carried out swiftly with minimal relaxation. It is also desirable to have alignment control in two or three directions, not confined alignment in a single direction. Accordingly there is a need for optical connectors which can provide rapid alignment or controlled misalignment.